1. Field of the Invention
The present invention generally relates to an image display device such as electronic paper and a portable display device, and a method for controlling the image display device.
2. Description of the Related Art
Highly-confidential images and the like in these types of image display devices may be browsed by others without permission and leaked out.
In electronic paper disclosed in Patent Document 1, a fingerprint pattern of a specific user who is authorized to use the electronic paper is recorded in advance. When a user starts operating the electronic paper, the user is required to touch his/her finger onto a fingerprint detector incorporated in the electronic paper to read a fingerprint pattern of the user. The personal identification is performed by comparing the fingerprint pattern of the user with the fingerprint pattern recorded in the electronic paper. When the user is identified as the authorized user by the personal identification, the user can display various images stored in the electronic paper on a display device. Further, in the case where personal identification is regularly performed when an image is being displayed on the display device, and a user is identified as the authorized user, the image is continuously displayed on the display device. When the user is not identified as the authorized user, the image displayed on the display device is erased.
In this manner, in the electronic paper disclosed in Patent Document 1, when a user is identified as the user authorized to use the electronic paper, an image is displayed on the display device. Accordingly, leakage of the image to others except for the specific user authorized to use the electronic paper is suppressed.    Patent Document 1: Japanese Patent Application Publication No. 2006-53688
Usually, images displayed on the electronic paper are browsed by only an authorized user. However, the image is sometimes required to be shared with others, such as by handing over the electronic paper displaying the image to a user unauthorized to use the electronic paper so that the unauthorized user can browse the displayed image. In this case, when the electronic paper disclosed in Patent Document 1 is used, the unauthorized user is not identified as the authorized user by the above-described regularly performed personal identification after the electronic paper is handed over to the unauthorized user. Therefore, the image displayed on the electronic paper is erased by the next regular personal authorization.
Here, the regular personal identification performed with an image displayed on the electronic paper may be set to be performed with a time interval which is long enough for the unauthorized user to browse the image after receiving the electronic paper. However, when the electronic paper displaying the image is left on a table and the like, the electronic paper keeps the display of the image until the next personal identification is performed. Therefore, there is a problem in that the image displayed on the electronic paper may be browsed by a third party and leaked out.
The present invention is made in light of the above-described circumstances and it is an object of at least one embodiment of the present invention to provide an image display device by which an image displayed on a device body of the image display device can be shared with a user unauthorized to use the image display device and leakage of the image can be suppressed.